Sealing arrangement for a gas turbine engine

ABSTRACT

The present invention relates to a sealing arrangement between a stator assembly and a rotor  12  of a gas turbine engine, the rotor  12  being rotatable about an engine axis, the stator assembly comprising vanes  22  provided at their radially inner ends with a vane support structure  28  which comprises an annular platform  30  supporting the vanes and a radial flange  32  which extends radially inwardly from the platform, the sealing arrangement comprising an array of leaves  36  which extend inwardly from the radially inner periphery of the flange  32,  towards a circumferential sealing surface  13  of the rotor  12.

The present invention relates to a sealing arrangement between a statorassembly and a rotor of a gas turbine engine, in particular, a sealingarrangement for sealing between compressor stator vanes and a compressordrum.

Gas turbine engines include an axial flow compressor comprising a rotorin the form of a compressor drum located within a substantially annularcasing. The compressor drum carries axially spaced sets of compressorblades, each set of compressor blades comprising a plurality of radiallyextending and circumferentially spaced rotor blades that rotate aboutthe engine axis. A set of non-rotating stator vanes is positioned ineach space between adjacent sets of compressor blades. Each set ofstator vanes comprises a plurality of circumferentially spaced vanesthat radially extend from the annular casing towards the compressordrum. It is necessary to seal between the radially inward end of eachstator vane and the compressor drum in order to prevent high-pressureair from circulating beneath the vanes.

In a known arrangement, for example as disclosed in GB 2426301, axiallyspaced and radially extending fins are provided on the compressor drumbetween adjacent sets of compressor blades. The stator vanes areprovided with an abradable liner, which the fins rub against in use,thereby providing a seal between the stator vanes and the compressordrum. Whilst this arrangement is satisfactory, it does not allow forlarge relative radial movement between the compressor drum and thestator vanes and does not allow for differential thermal expansion ofthe components, whilst maintaining a good seal. For example, in anextreme event, the compressor drum rotates eccentrically with respect tothe stator vanes, and the fins create a deep groove in the abradableliner. Subsequently, under normal running, the deep groove can provide aflow path beneath the vanes. This is undesirable.

Further, machining the fins on the compressor drum can be complicatedand time consuming and also the fins can serve as crack initiationpoints on the compressor drum. It is also necessary to replace theabradable liner periodically which results in an increased cost.

It is therefore desirable to provide a sealing arrangement betweenstator vanes and a rotor which provides a good seal at all conditions.

According to a first aspect of the present invention there is provided asealing arrangement between a stator assembly and a rotor of a gasturbine engine, the rotor being rotatable about an engine axis, thestator assembly comprising vanes provided at their radially inner endswith a vane support structure which comprises an annular platformsupporting the vanes and a radial flange which extends radially inwardlyfrom the platform, the sealing arrangement comprising an array of leaveswhich extend inwardly from the radially inner periphery of the flange,towards a circumferential sealing surface of the rotor.

The leaves may be directly attached to the radial flange. Alternatively,the leaves may be attached to a backing ring which is directly attachedto the radial flange. A further possibility is for the leaves to beformed on the radial flange by a material removal operation such asmachining or chemical etching, which removes the material between theleaves.

The annular platform may comprise a plurality of circumferentiallyarranged openings, each opening having the end of a stator vane locatedwithin it. The end of each stator vane may be attached to the annularplatform by upset forging.

In a preferred arrangement the annular vane support structure comprisesa plurality of circumferentially extending segments. Each segment maycomprise a projection that cooperates with an adjacent segment torestrict relative axial movement between adjacent segments.

The material of the rotor sealing surface may be hardened. For example,a hard coating may be applied to the rotor to form the sealing surface.

The rotor may be a compressor drum or disc and the vanes may becompressor vanes.

The invention also concerns a gas turbine engine comprising a sealingarrangement in accordance with any statement herein.

The invention may comprise any combination of the features and/orlimitations referred to herein, except combinations of such features asare mutually exclusive.

Embodiments of the present invention will now be described, by way ofexample only, with reference to the accompanying drawings, in which:

FIG. 1 schematically shows a sectional view of part of a compressorsection of a gas turbine engine;

FIG. 2 schematically shows an enlarged view of a stator vane arrangementof FIG. 1;

FIG. 3 schematically shows the view A of FIG. 2;

FIG. 4 schematically shows a view of a stator vane, vane support andleaf seal;

FIG. 5 schematically shows the view B of FIG. 4; and

FIG. 6 schematically shows the view C of FIG. 4.

FIG. 1 shows a compressor section 10 of a gas turbine engine. Thecompressor section 10 comprises a rotor in the form of a compressor drum12 having a plurality of axially spaced blade slots 14, 16. Compressorblades 18, 20, of successive stages of the compressor, are located inthe blade slots 14, 16 and the blades 18, 20 are circumferentiallyarranged around the drum. Although in this embodiment the blades 18, 20are located in blade slots 14, 16, they may be integrally formed withthe compressor drum or with a compressor disc or indeed located in otherknown blade securing arrangements such as, for example,circumferentially extending slots.

The compressor drum 12 is located within an outer casing 24 of thecompressor. A plurality of compressor stator vanes 22 are attached tothe outer casing 24 and are circumferentially arranged and extendtowards the compressor drum 12. The stator vanes 22 are situated betweenthe axially spaced sets of blades 18, 20. The radial inner ends 26 ofthe stator vanes 22 are attached to a vane support structure 28 which isannular and extends around the compressor drum 12. A leaf seal 34 isdisposed between the vane support 28 and the outer surface 13 of thecompressor drum and provides a seal therebetween. This leaf seal 34restricts the flow of high-pressure fluid underneath the radially inwardends 26 of the stator vanes 22.

With reference to FIGS. 2 and 3, the vane support 28 has a substantiallyL-shaped cross-section which comprises an annular axially extendingplatform 30 and a radially extending flange 32 that extends from oneaxial end of the platform 30 towards the compressor drum 12. The leafseal 34 comprises a plurality of thin metal leaves 36 (or leaf sealelements) circumferentially arranged in an annular pack. In thisembodiment, each leaf 36 is welded at its radially outer edge directlyto the inner periphery of the radially extending flange 32 of the vanesupport 28. The plurality of leaves 36 extend towards the compressordrum 12 and a free end (the radially inward end) of each leaf 36contacts an outer sealing surface 13 of the compressor drum 12. Theleaves 34 extend at an angle to the true radius and are resilientlydeformable such that they can bend, or flex, along their length. Forexample, the leaves may be inclined in the operative direction ofmovement of the sealing surface 13, in the radially inwards direction.The sealing surface 13 of the compressor drum 12 is constituted by ahard coating 15 in order to prevent the leaves 36 from abrading thesurface during use.

In other embodiments, the leaves 36 may be integrally formed with theflange 32 of the vane support structure 28 by either mechanicalmachining or chemical etching. Alternatively, the leaf seal 34 may beformed entirely separately from the vane support structure 28 byproviding a backing ring (not shown) with a plurality of leaves 36extending from it. The backing ring may then be attached to the radiallyextending flange 32 of the vane support structure 28 by welding, forexample. The leaf seal 34 may be formed as a continuous annular element,or more preferably, may be formed from a plurality of circumferentiallyextending leaf seal segments forming a continuous annulus.

In this embodiment the vane support structure 28 is formed from aplurality of circumferentially extending segments. The stator vanes 22are individually cast and are attached at a radially outward end to theouter casing 24 and at a radially inner end 26 to the axially extendingplatform 30 of the vane support structure 28. The axially extendingplatform 30 is provided with an opening 41 for each stator vane 22. Theradially inward end 26 of each stator vane 22 is located in a respectiveone of the openings 41 and is attached to the axially extending platform30 by hot upset forging. As will be readily apparent to one skilled inthe art, the stator vanes 22 may be attached to the vane support 28 byany other suitable method.

Although it has been described that the vane support structure 28 isformed from a plurality of circumferentially extending segments, inother embodiments the vane support structure 28 may be a continuousannular element. If the vane support structure 28 is formed from aplurality of circumferentially extending segments, the segments may beattached to one another by mechanical interlock, by welding, or by anyother suitable method.

FIGS. 4, 5 and 6 show a second embodiment of the present invention thatis similar to the embodiment of FIGS. 1-3. The radially inward ends 26of a plurality of stator vanes 22 are attached to a vane supportstructure 28. The radially outer end 25 of each stator vane 22 isprovided with an attachment portion 27 for attaching the stator vane 22to the outer casing 24 of the compressor. The vane support structure 28comprises an annular axially extending platform 30, to which theradially inward end 26 of each stator vane 22 is attached, and aradially extending flange 32. A leaf seal 34 is attached to the innerperiphery of the radially extending portion 32. As in the firstembodiment, the leaf seal 34 comprises a plurality of leaves 36 weldedat a first end to the radially extending flange 32. The leaves 36 extendat an angle to the true radius and are resiliently deformable such thatthey can bend, or flex, along their length. A free end (the radiallyinward end) of each leaf 36 is in contact with the sealing surface 13 ofthe compressor drum 12 in use.

The vane support structure 28 is a complete annulus that is formed froma plurality of circumferentially extending segments, each having aplurality of stator vanes 22 attached thereto, The end of the radiallyextending flange 32 of each vane support structure 28 segment isprovided with two circumferentially extending projections locatedaxially one on each side of the radially extending portion 32. As shownin FIG. 6, the projections 40, 42 extend each side of the radiallyextending flange 32 of an adjacent segment. This helps to restrictrelative axial movement between adjacent segments and seals againstaxial leakage between adjacent vane radially extending flanges 32.

In use, the compressor drum 12 and compressor blades 18, 20 rotate withrespect to the stator vanes 22, vane support 28 and leaf seal 34. Thefree ends of the leaves 36 are in contact with the sealing surface 13 ofthe compressor drum 12. This restricts the flow of high-pressure fluidunder the radially inward ends of the stator vanes 22 and thereforeprovides a good seal across each stage of the compressor. This in turnimproves the efficiency of the gas turbine engine. The leaves 34 are inconstant contact with the sealing surface 13 of the compressor drum 12.This ensures sealing at both transient and steady-state conditions. Ifthere is radial displacement, or differential expansion under thermal orcentrifugal effects, between the compressor drum 12 and the compressorstator vanes 22, then the leaf elements 36 can bend, or flex, alongtheir length such that they are always in contact with the sealingsurface 13 of the compressor drum 12.

The vane support structure 28 and leaf seal 34 can be manufacturedrelatively easily and inexpensively when compared to prior art sealingarrangements that rely on fins provided on the compressor drum thatabrade a liner provided on the stator vanes.

Although it has been described that the arrangement is for sealingbetween compressor stator vanes and a rotatable compressor drum, as willbe readily apparent to one skilled in the art, the invention may be usedto seal between any type of stator vane and rotor arrangement. Examplesinclude, but are not limited to, fans and turbines.

1. A sealing arrangement between a stator assembly and a rotor of a gasturbine engine, the rotor being rotatable about an engine axis, thestator assembly comprising vanes provided at their radially inner endswith a vane support structure which comprises an annular platformsupporting the vanes and a radial flange which extends radially inwardlyfrom the platform, the sealing arrangement comprising an array of leaveswhich extend inwardly from the radially inner periphery of the flange,towards a circumferential sealing surface of the rotor.
 2. A sealingarrangement according to claim 1, wherein the leaves are directlyattached to the radial flange.
 3. A sealing arrangement according toclaim 1, wherein the leaves are attached to a backing ring which isdirectly attached to the radial flange.
 4. A sealing arrangementaccording to claim 1, wherein the leaves are formed on the radial flangeby a material removal operation.
 5. A sealing arrangement according toclaim 1, wherein the annular platform comprises a plurality ofcircumferentially arranged openings, each opening having the end of astator vane located within it.
 6. A sealing arrangement according toclaim 5, wherein the end of each stator vane is attached to the annularplatform by upset forging.
 7. A sealing arrangement according to claim1, wherein the annular vane support structure comprises a plurality ofcircumferentially extending segments.
 8. A sealing arrangement accordingto claim 7, each segment comprises a projection that cooperates with anadjacent segment to restrict relative axial movement between adjacentsegments.
 9. A sealing arrangement according to claim 8, wherein theprojection is provided on the radial flange.
 10. A sealing arrangementaccording to claim 1, wherein the sealing surface is constituted by ahard coating on the rotor.
 11. A sealing arrangement according to claim1, wherein the rotor is a compressor drum or disc and the vanes arecompressor vanes.
 12. A gas turbine engine comprising a sealingarrangement in accordance with claim 1.